In the manufacture and processing of a moving web material, it is desirable to provide for the introduction of fluids, such as steam, to the web material in order to enhance the effect of various web-handling processes. For example, steam can be used to moisturize a web that has been over dried due to equipment in the web making or web handling process that tend to remove moisture from the web material during handling. It is known that condensation on the web material, due to the impingement of steam thereon, effectively increases the temperature of the web material and its effective moisture content. This is believed to effectively plasticize the web and make it easier and more susceptible to deformation. In addition, steam has been used to improve both the bulk generation and tensile efficiency of such embossing procedures that impart a high definition embossment. Such steam processes have been used in the processing of air laid substrates, single ply wet laid substrates, dual ply wet laid substrates, non-woven substrates, woven fabrics, and knit fabrics.
Numerous processes for the application of steam to a web material are known in the art. For example, parent rolls of creped base sheet materials can be unwound and passed over a steam boom prior to embossing the web material between matched steel embossing rolls. In such a process, high quality steam is supplied to an application boom at anywhere from 5 psi to 10 psi. A typical boom is constructed from stainless steel pipe, capped on one or both ends, that is provided with a plurality of nozzles. The nozzles are capable of providing a spray of steam upon a passing web material as the web material passes proximate to the steam boom. An exemplary process utilizing such an application is described in U.S. Pat. No. 6,077,590.
However, such an application can have significant drawbacks. For example, the steam is applied to the passing web material in an ambient environment. This can allow steam that does not impinge upon the web material to be released to the ambient atmosphere and then condense upon the processing equipment. Such condensation can cause the appearance of rust upon processing equipment. This can then shorten the lifespan of expensive processing equipment. In addition, the impingement of steam upon the passing web material can cause debris resident upon the web material to dislodge. This dislodged debris is then airborne and can be deposited upon the damp processing equipment. Such a collection and buildup of debris increases the risk of product contamination, or otherwise increases the frequency and effort required to clean and maintain the processing equipment. Additionally, not all steam emanating from the stainless steel pipe is effectively deposited upon the passing web material. If one were to consider a steam molecule as a particle, the steam particle, upon release from the steam boom, is provided with sufficient momentum to enable it to rebound off the web material or pass through the web material to the ambient atmosphere surrounding the web material. This does not provide any heating effects upon the web material. This may provide insufficient heat to the web material in order to facilitate any plastic deformation that may be required due to the needs of any downstream processing. In sum, these processes are simply not efficient.
There are other systems for applying steam to a web material that have higher stated efficiencies. However, these systems tend to be unnecessarily complex. For example, some systems provide a pair of dripless steam boxes arranged above and below the plane of a passing web material. The steam boxes are generally closely embraced and enclosed by a steam chamber housing. The steam chamber housing momentarily confines a billowing steam in the immediate vicinity of the web material. Excess steam is removed by way of a downdraft exhaust system. Such steam processing systems are disclosed in U.S. Pat. No. 3,868,215. The incorporation of such complex processing equipment into a web material processing system is generally not financially feasible.
Therefore, it would be advantageous to provide for the application of a fluid, such as steam, to a passing web material in a cost effective and non-complex manner. It is in this way that a web material can be heated and moisturized in order to facilitate plastic deformation. Increasing the ability of a web material to plastically deform facilitates the downstream treatment of the treated web material for embossing, compaction, softening, and contraction.